Before the beginning of every cricket match, I have seen each and every player from both the sides are accompanied by a child. Why exactly are they accompanied by children ?
I think it is a tradition followed from other sports like football. See the same question in football. Why do players enter with children on the ground?
Basically, it generates more money & more viewership.
Some points to highlight the end result: If a match starts at 10 AM, then TV programs can start at 9:30 AM, covering the pitch-inspection, the coin-toss, etc. Here the walk-in ceremony will add program time and ADvertisement time on TV. By including some more extras, the TV show can start at 9 AM. Selection of the children maybe by some contest (make money via SMS, or sales of promotional burgers or drinks etc). The selected children will publicise this with school mates and neighbours, who will be waiting to watch on TV.
We can even consider the walk-in as a mini opening ceremony. If the World Cup Opening Ceremony attracts eyeballs (+ AD money), then the children also attract a small amount of eyeballs (+ AD money).
Even though it is basically a financial choice, now-a-days it can be used for political purposes too, eg by selecting minorities or by supporting some school.